Stocks & Shares ISA Platform Fees: How to Compare Them Properly (2026)
Platform fees, fund ongoing charges and trading costs can quietly erode ISA returns by thousands over a lifetime. Here's a structured way to compare stocks and shares ISA platforms in 2026.
The three layers of ISA cost
Every stocks and shares ISA has at least three potential cost components, and providers differ enormously in how they structure and disclose them:
- Platform (account) fee — charged by the ISA provider for holding your investments, often 0.15%-0.45% of assets per year, or a flat monthly/annual fee.
- Fund ongoing charge (OCF) — charged by the fund or ETF manager, entirely separate from the platform, typically 0.05%-0.20% for passive index trackers and 0.5%-1%+ for actively managed funds.
- Trading fees — a per-trade charge for buying or selling shares, investment trusts or ETFs, commonly £0-£12 per trade, though usually £0 for buying open-ended funds.
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Providers structure their platform fee in one of two ways, and the "better" structure depends entirely on your portfolio size.
| Portfolio size | Percentage fee (e.g. 0.25%) annual cost | Flat fee (e.g. £120/year) annual cost | Cheaper option |
|---|---|---|---|
| £5,000 | £12.50 | £120 | Percentage |
| £20,000 | £50 | £120 | Percentage |
| £50,000 | £125 | £120 | Roughly equal |
| £100,000 | £250 | £120 | Flat fee |
| £250,000 | £625 | £120 (or capped elsewhere) | Flat fee |
The crossover point — where a flat fee becomes cheaper than a percentage fee — typically sits somewhere between £40,000 and £70,000, depending on the exact rates on offer. If you're consistently using the full £20,000 annual ISA allowance, your portfolio will likely cross that threshold within a few years, so it's worth choosing a platform that suits where your ISA is heading, not just where it starts.
Fund ongoing charges matter as much as the platform fee
The fund OCF is charged regardless of platform and is easy to overlook because it's deducted within the fund's unit price rather than as a separate line on your statement.
| Fund type | Typical OCF |
|---|---|
| Passive global tracker fund | 0.05% – 0.15% |
| Passive UK/US index tracker | 0.05% – 0.20% |
| Actively managed multi-asset fund | 0.50% – 1.00% |
| Actively managed sector/specialist fund | 0.75% – 1.50%+ |
A portfolio built from low-cost passive trackers can have a total OCF under 0.15%, while a portfolio of actively managed funds can easily average 0.8%-1% — a gap that compounds significantly over decades, independent of which platform holds the investments.
Worked example: the compounding cost of fees
Consider £100,000 invested for 25 years, growing at 6% gross annual return, comparing a low-cost portfolio (0.25% total annual cost) against a higher-cost portfolio (0.75% total annual cost) — a 0.5 percentage point difference.
| Scenario | Net annual growth | Value after 25 years (approx.) |
|---|---|---|
| Low-cost (0.25% total fees) | 5.75% | ~£401,000 |
| Higher-cost (0.75% total fees) | 5.25% | ~£355,000 |
| Difference from 0.5pp fee gap | ~£46,000 |
The 0.5 percentage point difference — which sounds negligible year to year — compounds into a difference of roughly £46,000 over 25 years on this example, purely from cost drag, assuming identical underlying gross returns.
A practical comparison checklist
When comparing stocks and shares ISA platforms, work through these in order:
- Platform fee structure — percentage, flat, or tiered/capped — and where your portfolio size sits relative to the crossover point.
- Fund/ETF trading fees — free, or a fixed cost per trade, and how often you expect to trade.
- Fund ongoing charges — check whether your chosen platform gives access to the lowest-cost share classes of your preferred funds (some platforms only offer more expensive "retail" share classes).
- Exit fees — some platforms charge to transfer your ISA out; this shouldn't be a deciding factor but is worth knowing.
- FX fees — relevant if you plan to hold overseas shares or funds denominated in foreign currency.
Buy-and-hold vs active trading profiles
| Investor type | Fee priority |
|---|---|
| Long-term, buy-and-hold fund investor | Platform fee structure + fund OCF matter most; trading fees barely matter |
| Frequent individual share trader | Per-trade fees matter most; platform percentage fee matters less if it's capped |
| Mixed portfolio (funds + shares) | Compare total blended cost across a realistic year of your actual trading pattern |
There is no single "best" platform for everyone — the right choice depends on your portfolio size, how often you trade, and whether you invest in individual shares, funds, or a mix. Always model the total annual cost on your specific portfolio size and trading pattern, not the headline fee alone.
Use our ISA calculator to check your annual allowance usage, and the compound interest calculator to model how different fee levels compound over your investing timeframe.
Frequently asked questions
What's the difference between a platform fee and a fund ongoing charge?
The platform fee (or 'account fee') is charged by the ISA provider for holding and administering your account, typically as a percentage of assets or a flat monthly fee. The fund ongoing charge (OCF) is charged separately by the fund manager for running the underlying investment, regardless of which platform holds it.
Are percentage-based platform fees or flat fees cheaper?
It depends on your portfolio size. Percentage fees are usually cheaper for small portfolios but become expensive as your ISA grows into tens of thousands of pounds, at which point a flat monthly or annual fee, often capped, tends to work out cheaper.
Do I pay trading fees inside a stocks and shares ISA?
Many platforms charge a fee per trade for buying or selling individual shares or ETFs (often £0-£12), though most do not charge to buy or sell open-ended funds. Frequent traders should weight trading costs heavily; buy-and-hold investors should weight the ongoing platform and fund fees more heavily.
How much difference can fees make over 20-30 years?
A 0.5 percentage point difference in total annual costs on a £100,000 portfolio growing at 6% a year can amount to tens of thousands of pounds less by retirement, purely from lost compounding, even though 0.5% sounds trivial year to year.
Does the annual ISA allowance affect which platform I should choose?
Not directly, but if you're maximising the £20,000 annual allowance, your ISA will likely become a large portfolio over time, making percentage-based fees increasingly expensive relative to flat-fee alternatives — factor in your expected trajectory, not just your starting balance.
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